Manufacture of compound sheets of glass and cellulose derivative composition



U adherently secured to two tact, the glass sheets and Patented June 9,1931 UNITED STATES WILLIAM JOHNSTON, OF

ASHFORD, ENGLAND, ASSIGNOR'TO ACETEX SAFETY GLASS LIMITED, 01? LONDON,ENGLAND MANUFACTURE OF COMPOUND SHEETS 0F GLASS AND CELLULOSE DERIVATIVECOMPOSITION Ho Drawing. Application filed July 2, 1929, Serial No.375,594, and in Great Britain March 4,

This invention relates to the manufacture of compound sheets, comprisinga sheet of cellulose derivative composition, such as cellulose acetate,interposed between and sheets of glass. According to the invention, twosheets of glass are caused to adhere to'an interposed sheet of cellulosesuch as cellulose acetate, by moistening the 10 surface of the cellulosederivative composition sheet with a plasticizer or solvent of highboiling point; initially pressing together the three sheets by an inertgas under pressure, so that they are in direct, close, surface conedgesof all the sheets being freely exposed to the gas; and finallysubjecting the sheets to steam under pressure. The steam is at atemperature less than the boiling point of the plasticizer or solvent,and the sheets are similarly freely exposed to the steam as they were tothe inert gas.

Prior to subjecting the sheets to gas and steam pressure, superflousliquid and air are eliminated. This can be done by passing the sheetsbetween rubber faced rollers.

The gas and steam pressure treatments can be effected in an autoclaveinto which compressed air is admitted to effect the initial pressing andsubsequently the steam to eflect the final pressing.

A suitable pla-sticizer for use with cellulose acetate is triacetin.

A representative example of one way of carrying out the above describedprocess is as follows: I

A sheet of cellulose acetate, which has been previously moistened withtriacetin by immersion in a bath thereof, is interposed between twosheets of glass. and the three sheets p are first rolled between rubberfaced rollers to express air and excess liquid from between the sheets.The combined pack of sheets is then. placed in a closed chamber andsubjected to the direct pressure of compresse air at a pressure ofapproximately 50 pounds absolute per square inch for a period of 15minutes. After slight relaxation of the air pressure, steam at apressure of approximately 50 pounds absolute to the square inch isleased, not unduly rapidly,

derivative composition, 1

then admitted to the closed chamber, and the pack of sheets is subjectedto the pressure and temperature of the steam for a period of 15 minutes.The gaseous pressure is then reand the adhering sheets are then removedfrom the chamber.

The temperature of steam at the above )ressure is below the boilingpoint of triacetin which is 258 C. at atmospheric pressure.

The above mentioned pressures and periods can be varied somewhat withoutmaterially affecting the resultant product.

Claims:

1. A process for effecting the interadherence of two sheets of glass toan interposed sheet of cellulose derivative composition, consisting inmoistening the surface of said cellulose derivative composition sheetsolely with a plasticizer of high boiling point, initially freelyexposing and pressing together said glass sheets with said moistenedcellulose derivative composition sheet interposed in a gas underpressure inert to said cellulose derivative composition sheet, andfinally freely exposing and pressing said sheets in steam under pressureand at a temperature lower than the boiling point of said plasticizer.

2. A process for ence of two sheets effecting the interadherof glass toan interposed sheet of cellulose derivative composition, consisting inmoistening the surface of said cellulose derivative composition sheetsolely with a plasticizer of high boiling point, initially freelyexposing and pressing together said glass sheets with said moistenedcellu* lose derivative composition sheet interposed in compressed air,and finally freely exposing and pressing said sheets in steam underressure and at a temperature lower than the boiling point of saidplasticizer.

3. A process for effecting the interadheronce of two sheets of glass toan interposed sheet of cellulose acetate, consisting in moistening thesurface of said cellulose acetate sheet solely with triacetin, initiallyfreely exposing and pressing together said glass sheets with saidmoistened cellulose acetate sheet interposed in a gas under pressureinert to said cellulose acetate sheet, and

finally freely exposing and pressing said sheets in steam under pressureand at a temperature lower than the boiling point of said triacetin.

4. A process for effecting the interadherence of two sheets of glass toan interposed sheet of cellulose acetate, consisting in moistening thesurface of said cellulose acetate sheet solely with triacetin, initiallyfreely exposing and pressing together said glass sheets with saidmoistened cellulose acetate sheet interposed in compressed air, andfinally freely exposing and pressing said sheets in steam under pressureand at a temperature lower than the boiling point of said triacetin.

5. A process for effecting the interadherence of two sheets of glass toan interposed sheet of cellulose derivative composition, consisting inmoistening the surface of said cellulose derivative composition sheetsolely with a plasticizer of high boiling point, initially freelyexposing and pressing together said glass sheets with said moistenedcellulose derivative composition sheet interposed in a gas underpressure inert to said cellulose derivative composition sheet, slightlyrelaxing the pressure of said inert as, and finally admitting to saidgas under relaxed pressure steam under pressure and at a temperaturelower than the boiling point of said plasticizer.

6. A process for effecting the interadherence of two sheets of glass toan interposed sheet of cellulose derivative composition, consisting inmoistening the surface of said cellulose derivative composition sheetsolely with a plasticizer of high boiling point, initially freelyexposing and pressing together said glass sheets with said moistenedcellulose derivative composition sheet interposed in compressed air,slightly relaxing the pressure of said compressed air and finallyadmitting to said compressed air under relaxed pressure steam underpressure and at a temperature lower than the boiling point of saidplasticizer.

7. A process for effecting the interadherence of two sheets of glass toan interposed sheet of cellulose acetate, consisting in moistening thesurface of said cellulose acetate sheet solely with triacetin, initiallyfreely exposing and pressing together said glass sheets with saidmoistened cellulose acetate sheet interposed in a gas under pressureinert to said cellulose acetate, slightly relaxing the pressure of saidinert gas, and finally admitting to said gas under relaxed pressuresteam under pressure and at a temperature lower than the boiling pointof said triacetin.

8. A process for effecting the interadherence of two sheets of glass toan interposed sheet of cellulose acetate, consisting in moistening thesurface of said cellulose WILLIAM JOHNSTON.

